Horizontal injection molding machines mainly comprise a mold clamping apparatus for clamping a mold, and an injecting apparatus for injecting a resin material into the clamped mold. The mold clamping apparatus includes a fixed platen for supporting a fixed mold, a movable platen for supporting a movable mold, and a mold clamping cylinder for pressing the movable platen toward the fixed platen, as disclosed, for example, in Japanese Patent Application Laid-Open Publication No. (JP-A) H05-329900.
The prior art invention disclosed in JP H05-329900A will be described below with reference to FIG. 11 hereof. As shown in FIG. 11, a conventional mold clamping apparatus 100 includes a fixed platen 102 fixedly mounted on a base 101, a mold clamping cylinder 103 horizontally movably disposed on the base 101, tie bars 104, 104 extending horizontally between the mold clamping cylinder 103 and the fixed platen 102, a movable platen 106 guided by the tie bars 104, 104 and connected to a piston rod 105 of the mold clamping cylinder 103, and nuts 107, 107 threadedly mounted on the tie bars 104, 104, respectively, for restricting movement of the mold clamping cylinder 103.
Additionally, a rail 108 is laid on the base 101, and sliders 109, 110 as sliding members are slidably fitted with the rail 108. The slider 109 supports the mold clamping cylinder 103, and the slider 110 supports the movable platen 106.
A fixed mold 111 is attached to the fixed platen 102, and a movable mold 112 is attached to the movable platen 106. After the movable mold 112 is in abutment with the fixed mold 111, the mold clamping cylinder 103 is expanded. The movable platen 106 is thereby pressed toward the fixed platen 102, and thus mold clamping is performed.
At the time of mold clamping, a mold clamping reaction force equal to a mold clamping force is produced. By the mold clamping reaction force, the mold clamping cylinder 103 is bent as shown by an imaginary line A. Note that the imaginary line A is emphasized herein to facilitate understanding. Due to the bend of the mold clamping cylinder 103, the slider 110 is inclined at an angle α.
FIG. 12 is a cross-sectional view taken along line 12-12 of FIG. 11. As shown in FIG. 12, the slider 109 having an inverted U-shaped cross section is mounted on the rail 108 having a rectangular cross section. In this structure, floating of the slider 109 from the rail 108 is allowed. However, in this structure, the rail 108 and the slider 109 are in surface contact with each other. By this surface contact, a large frictional resistance is generated between the rail 108 and the slider 109.
In the mold clamping apparatus 100 shown in FIG. 11, when the mold is replaced, the nuts 107, 107 are loosened, the slider 109 is moved to change the position of the mold clamping cylinder 103, and the nuts 107, 107 are tightened.
When the frictional resistance between the rail 108 and the slider 109 is large, energy required for moving the slider 109 becomes large, and accordingly the operation cost is increased. It is therefore necessary to reduce the frictional resistance.
An example of measures for reducing the frictional resistance will be described below with reference to FIG. 13. As shown in FIG. 13, steel rolling elements 113 are built in between the rail 108 and the slider 109. The steel rolling elements 113 are steel balls or steel rollers. Since frictional resistance in rolling contact is approximately one-tenth of that in surface contact, when the steel rolling elements 113 are used, the frictional resistance can be greatly reduced. Thus, such a structure is preferred in recent years.
Hereinbelow, this mechanism consisting of the rail 108, the slider 109 and the rolling elements 113 will be referred to as “linear guide mechanism with built-in rolling elements”.
When the slider 110 is inclined at the angle α as shown in FIG. 11, the rolling elements 113 shown in FIG. 13 undergo an undesirable posture change, that is, a twist. This would result in operational failure or breakage of the rolling elements 113. Thus, in conventional technique, the linear guide mechanism with the built-in rolling elements shown in FIG. 13 cannot be adopted, or even if it is adopted, its service life will be short.
However, since there is a demand to reduce facility cost and operation cost, an improved structure of the mold clamping apparatus is needed for adopting the linear guide mechanism with the built-in rolling elements.